Steering columns for automotive vehicles are often equipped with various adjustments that enable the operator of the vehicle to position and lock the column in any of a number of positions. Some columns includes brake and telescope adjustment to enable the operator to adjust the angle of the column as well as the fore and aft telescope position of the hand wheel.
Current designs are using compression springs, torsion springs or a bending leaf spring which applies the load in the area of the rake mechanism. Due to packaging and position the springs will have to deflect a large percentage of its full capacity. Therefore, the spring force varies greatly. The driver experiences a change of rake effort when going from full down to full up.
FIG. 1 shows a prior art telescoping column assembly having an upper jacket 12 which telescopes relative to a lower jacket 14. The column 10 is mounted on a bracket 16 of a vehicle chassis by a pivot bolt 18 to enable the column assembly 10 to pivot or rake about a transverse axis 20 of the pivot bolt 18 for adjusting the up and down movement of the column assembly 10. A rake mechanism 22 is carried on a column bracket 24 that is fixed stationarily to structure the vehicle and includes a rake bolt 26 extending through the bracket 24 and through an associated sliding bracket 28 fixed to the upper column 12 and slideable therewith relative to the bracket 24 during telescopic movement of the upper column 12. The rake mechanism 22 serves to lock and release, respectively, the column assembly 10 in a selected position of pivotal adjustment about the pivot bolt 18. When the rake mechanism 22 is operated to unlock the column assembly 10, the column assembly 10 is free to pivot about the axis 20 of the pivot bolt 18. In order to counteract the weight of the column assembly 10 when the rake mechanism is unlocked, a compression spring 30 acts between the mounting bracket 24 and sliding bracket 28. The compression spring 30 applies an upward force on the sliding bracket 28 to counteract the gravitational force of the weight of the column 10 pivoting about the pivot bolt 18 when the rake mechanism 22 is released. It will be seen that the compression spring 30 is spaced from the axis 20 of the pivot bolt 18 and thus must be compressible over a considerable distance to provide spring assist during the full movement of the column assembly 10 about the pivot bolt 18. Due to the inherent spring constant characteristic of coil springs, the spring 30 offers a greater counteracting lifting force to the column assembly 10 when in a lowered position as compared to when the column assembly is pivoted upwardly to a raised position, increasing the distance between the bracket 24 and sliding bracket 28 and thus opening the gap across which the spring 30 must span. Inherently, an operator will notice a variable effort in positioning the column assembly 10 up or down about the pivot bolt 18. With the compression spring 30 situated out from the pivot bolt 18, it is likely that the column assembly 10 might be in equilibrium (i.e., requiring no lifting or lowering force by the operator) somewhere near the middle position of the up and down column travel. To lower the column 10 from such equilibrium position, an operator must overcome the counteracting lifting force of the spring 30, requiring application of considerable downward force (about 80-100 N) to rake the column 10 down from the equilibrium middle position. Similarly, if the operator wishes to move the column from the equilibrium middle position upwardly, the operator will have to apply a similar lifting load (i.e., 80-120 N) to rake the column 10 up.
Since the spring 30 acts constantly between the bracket 24 and the sliding bracket 28, it necessarily introduces a certain amount of frictional resistance to the telescoping movement of the upper column 12 and sliding bracket 28 relative to the bracket 24. This frictional dragging effect of the spring 30 against the sliding bracket 28 introduces extra effort by the operator to telescope the column assembly 10. The present invention provides a spring assist arrangement which overcomes or greatly minimizes the foregoing limitations of the prior art.